It’s clear that many existing laws have little or no effect on behavior.  An even larger class of laws have little or no effect on most people’s behavior.  What are the main mechanisms of legal irrelevance?

1. People know the law is not enforced.  Anti-cohabitation laws in modern Virginia are a good example.  If you can shamelessly break the law with impunity, the law effectively doesn’t exist.

2. People have no desire to break the law.  Suicide laws are a good example for most of us.  If you wouldn’t choose to do X even in the absence of punishment, you’re not going to do X in the presence of punishment.

3. People don’t want to enforce the law.  Laws against stealing from your parents are a fairly good example.  They’re safe targets because they love you too much to call the cops.

4. Enforcing the law is more trouble than it’s worth.  Lawsuits for small sums are probably a good example (unless you’re in a loser-pays regime).  If there’s a $200 fixed cost of going to small claims court, the right to sue for $5 of damages is basically moot.  The same applies if threatening legal action foreseeable leads to a breakdown of more valuable cooperation and/or reputation.

5. A clearly cheaper enforcement mechanism exists. Calling the cops and/or suing people are often obviously inferior to e.g. disowning, firing, ostracizing, yelling, or the silent treatment.  So while breaking the law is costly, legal punishment is not the relevant cost.

I know, of course, that there’s a continuum of legal irrelevance.  But you get the idea.  Are there any important mechanisms I’m missing?